In particular in the processing of plastics, it is often reasonable to provide two or several successive extruders, each of which performing individual processing steps. For example, when plastic material is used in the form of powder, inlet and melting of the powder can take place in a first extruder. Homogenizing and pressure build-up then takes place in a second, downstream extruder. Successive extruder arrangements of the generic type are known for example from EP 1 005 411 B1, U.S. Pat. No. 3,261,056 and DE 2 304 088 A. The known plants are distinguished by the fact that additional process steps that must be performed between the two extruders are hard to integrate. The term ‘materials’ is to be understood as fundamentally free flowing materials that are treatable in screw-type extruding machines.